1. Field of the Invention
This invention relates to a miniature current-controlled actuator in which when a stator coil is energized, a rotor with a permanent magnet is rotated through a preset angle in a direction corresponding to a direction in which the stator coil is energized.
2. Description of Related Art
In the technical field of a camera, a miniature current-controlled actuator, sometimes referred to as a moving-magnet motor, is known. This actuator is constructed so that when a stator coil is energized, a rotor with a permanent magnet is rotated within the range of a preset angle in a direction corresponding to a direction in which the stator coil is energized, and an output pin actuated integrally with the permanent magnet drives a member to be driven. The actuator, in contrast with a stepping motor, has significant advantages of affording low cost, compactness, and small power consumption. Thus, in the camera, it is chiefly used as a driving source for shutter blades or stop blades, but its application is not limited to the camera and can be made to various products.
For such actuators, various structures have been proposed and used, and typical examples of the structures in recent years are set forth in Japanese Patent Kokai Nos. 2000-197326 and 2000-292827. The actuators described in these publications are such that although the structures of stators, as well as those of rotors, are different from each other, magnetic poles magnetized in the radial direction of individual permanent magnets are equal in number, and even though the rotors are replaced with each other, they will function properly, insofar as they gives rise to no shape or dimension problems. Although, for the rotor, one described in the former publication appears to be simpler in fabrication, it entails the high cost of material and is hard to obtain a great magnetic force (high magnetic flux density). Consequently, in most cases, one described in the latter publication is used as an actuator for cameras.
Here, the structure of the rotor of this type will be specifically explained. The permanent magnet magnetized in the radial direction has a cylindrical shape. A rotary shaft which lies in a hollow portion of the permanent magnet and whose ends projecting therefrom are supported by bearings of the stator and an output pin (driving pin) located in the radial direction are integrally constructed of synthetic resin. Such an output pin is often provided as a single one. Even with the use of the actuator in the camera, however, two output pins may be provided at symmetrical positions of 180xc2x0, depending on the structure of the shutter blades or the stop blades, and the number of pins can be chosen properly in accordance with a desired specification. Such a component part made of synthetic resin, after being fabricated as an independent member, may be attached to the permanent magnet by cementation or force fit. In view of cost, however, it is advantageous to attach the component part to the permanent magnet on molding the component part through a so-called outsert process of injection molding.
For this actuator also, the need for further compactness has recently been emphasized. However, in the actuator of the type set forth in the above Kokai No. 2000-292827, the outside diameter of a cylindrical stator has already been reduced to as small as 4-5 mm, and the permanent magnet of the rotor has also been reduced to as small as 2 mm in diameter. Thus, the situation is that further compactness is extremely difficult. In particular, in the permanent magnet of the rotor, even when such a small diameter is slightly reduced, the proportion of a reduction in mass is increased, and it becomes difficult to ensure a preset magnetic force or to positively obtain permanent magnets within tolerances for mass production. As such, when an attempt is made to achieve further compactness, the problem arises that cost is greatly increased.
It is thus conceivable that the permanent magnet is configured into a column shape so that even when the diameter is reduced, mass which remains unchanged can be ensured. When the permanent magnet is configured into a column shape without reducing the diameter, a great magnetic force is necessarily obtained. In such a case, however, a question arises as to how portions supported by the bearings and the output pin are constructed. In order to solve this, the structure that the portions supported by the bearings and the output pin are fabricated as independent parts of special shapes so that the permanent magnet is attached to them by cementation or force fit has been proposed. However, as parts diminish in size, it becomes difficult to set up the parts, one by one, by cementation or force fit and to positively produce good rotors, and actuators thus fabricated involve high cost as a matter of course.
It is, therefore, an object of the present invention to provide a miniature, low-cost current-controlled actuator in which a stator coil is supplied with a current and thereby a rotor is rotated within the range of a preset angle in a direction corresponding to a direction in which the stator coil is supplied with the current, so that the rotor is fabricated integrally with portions supported by bearings and an output pin with respect to a column-shaped permanent magnet, through a synthetic-resin injection molding process.
In order to achieve the above object, the actuator of the present invention is constructed so that the rotor is rotated within the range of a preset angle in a direction corresponding to the direction of current supply to the stator coil. In this case, the rotor includes a column-shaped permanent magnet having surfaces perpendicular to a center line of rotation and a surface surrounding the center line of rotation and a frame body configured integrally with the permanent magnet. The frame body covers two center portions of rotation of the permanent magnet and the surface surrounding the center line of rotation of the permanent magnet so that a plurality of exposed surfaces are provided. Each of areas in which these center portions of rotation are covered is provided with a journal supported by the bearing of the stator, and a portion extending in the radial direction from one of the center portions of rotation is provided with the output pin to be parallel to the center line of rotation.
In the actuator of the present invention, at a place where each of the center portions of rotation of the permanent magnet is opposite to the frame body covering each center portion, a polygonal concavity, on one hand, is provided, and on the other hand, a convexity is configured to project into the concavity and occupy it. By doing so, the permanent magnet is favorably constructed integrally with the frame body.
Further, in the actuator of the present invention, at a place where a surface surrounding the center line of rotation of the permanent magnet is opposite to the frame body covering the surface, concavities, on one hand, are provided, and on the other hand, convexities are configured to project into the concavities and occupy them. By doing so, the permanent magnet is favorably constructed integrally with the frame body.
Still further, in the actuator of the present invention, the permanent magnet is magnetized as two magnetic poles in the radial direction, and at least one of the surfaces perpendicular to the center line of rotation has a groove configured along the boundary between the two magnetic poles. The frame body is partially provided in the groove, and the output pin is situated on an extension line of the boundary. Whereby, not only is the integration of the permanent magnet with the frame body favorably maintained, but also the positioning of the output pin in the direction of magnetization becomes very easy, in view of fabrication.
In the actuator of the present invention, when the frame body is constructed so that the output pin and another output pin are located at symmetrical positions of 180xc2x0 of the permanent magnet, applications different from the case of a single output pin can be found.
This and other objects as well as the features and advantages of the present invention will becomes apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.